function Search(obj) {
    var str = ``
    for (const key in obj) {
        str +=`${key}=${obj[key]}&`    
    }
    return str.slice(0, str.length - 1)
}
function ajax(method, url, params, cb) {
    var xhr = new XMLHttpRequest()
    xhr.open(method, method == 'get' ? url + '?' + Search(params) : url)
    xhr.onreadystatechange = function () {
        if (xhr.readyState==4) {
            cb(JSON.parse(xhr.responseText))
        }
    }
    xhr.setRequestHeader('content-type', 'application/x-www-form-urlencoded')
    xhr.send(method == 'get' ? null : Search(params))
}
